1. Field of the Invention
The present invention relates to a sealing device for a reciprocating shaft which seals an axial periphery of the reciprocating shaft, for example, a piston rod of a hydraulic shock absorber of a vehicle or the like.
2. Description of the Conventional Art
As a typical prior art of the sealing device for the reciprocating shaft used in the hydraulic shock absorber of the vehicle, for example, there is a structure described in Japanese Unexamined Patent Publication No. 10-82467, (patent document 1) and Japanese Unexamined Patent Publication No. 2000-46092, (patent document 2).
FIG. 5 is a half sectional view showing a conventional sealing device 100 for a reciprocating shaft of the same kind as described in the patent document 1 mentioned above by cutting along a plane passing through an axis together with a part of the hydraulic shock absorber. In particular, the sealing device 100 is structured such that a main lip 102, a dust lip 103 and an outer peripheral lip 104 are integrally formed by a rubber-like elastic material with a metal washer 101 held between a caulked end portion 110a of a cylinder 110 of the hydraulic shock absorber and a rod guide 111. The main lip 102 and the dust lip 103 are brought into slidable contact with an outer peripheral of a rod 112 corresponding to a reciprocating shaft, and the outer peripheral lip 104 is brought into slidable contact with an inner peripheral surface of the cylinder 110.
Since the sealing device 100 provided with the structure mentioned above integrally has the main lip 102, the dust lip 103 and the outer peripheral lip 104 made of the rubber-like elastic material, in the washer 101, the sealing device 100 can be inexpensively provided. In the structure mentioned above, it is effective to make an inner diameter of the washer 101 small so as to be close to an outer diameter of the rod 112, as a method of improving a pressure tightness of the main lip 102 for sealing a working fluid inside the hydraulic shock absorber. However, there is a limit to make the inner diameter of the washer 101 small, in view of formability of the main lip 102.
Accordingly, in order to sufficiently improve the pressure tightness of the main lip 102, it is effective to support a back face side and an inner peripheral side of the main lip by a backup ring made of a synthetic resin, as described in the patent document 2. However, since the backup ring is held between an oil seal having the main lip and a dust seal provided in the washer in an outer side of the oil seal, the number of parts is increased and troublesomeness is caused in an assembling work.